Abstract: A device for a fuel system for a combustion, engine (M), in which a validation unit (V) is connected to a supply line (L) between a fuel reservoir (D) and the combustion engine (M), including means (DR2) for recording the fuel consumption of the combustion engine (M); a data storage medium (S); means (DR2) for sampling the fuel flowing to the combustion engine (M); means (A) for analysing the characteristic fuel features. Methods are also described for controlling the supply of fuel to a combustion engine (M) related to defined emission levels of combustion products of the type CO2, NOx and CO and also solid particles.